Since carbon nanotubes (CNTs) were first discovered by Iijima [S. Iijima, Nature Vol. 354, P. 56 (1991)], thorough research therein has been being conducted. CNTs have potential properties which are not found in conventional materials, including the high elastic modulus of about 1.0˜1.8 TPa, heat resistance capable of enduring heat at about 2800° C. in a vacuum, high thermal conductivity about two times that of diamond and high current mobility about 1000 times that of copper. Thus, CNTs are considered to be highly applicable in the entire field including nano-sized electrical devices, electronic devices, nano-sensors, optoelectronic devices, high functional composites and so on.
However, CNTs are problematic in that they are very difficult to disperse in a polymer resin owing to the long cylindrical shape thereof. Accordingly, a dispersant may be used, but the dispersion of CNTs is still difficult despite the use of a dispersant.
In conventional photoelectrochemical devices including CNTs, CNTs are used in a manner such that CNTs are layered on a polymer resin substrate using physical vapor deposition (PVD) including sputtering, ion plating or vacuum evaporation or chemical vapor deposition (CVD). However, this manner may cause problems including the use of a complicated apparatus, poor productivity, and difficulty of continuously applying CNTs on a large substrate.
With the goal of solving the aforementioned problems, a method of manufacturing a coating film containing CNTs has been developed (Japanese Patent No. 3665969), the method including applying a first dispersion containing CNTs dispersed therein on a substrate, removing the solvent, and applying a second dispersion containing a polymer resin and a solvent so that the second dispersion infiltrates a three-dimensional network structure of CNTs, thus manufacturing the coating film containing CNTs. However, this method is very disadvantageous because CNTS are easily separated upon treatment with a chemical or a solvent for application to electronic devices, electrical devices, etc.
Also, a method of manufacturing a conductive film through chemical bonding between CNTs having —COOH and a surface of a polymer resin film having —NH has been developed (Korean Patent Application No. 10-2006-0032812). In this case, however, the CNTs exposed to the surface of the film easily separate therefrom due to a mechanical force such as a surface frictional force occurring in the process, negatively affecting electrical properties (surface resistivity) of the conductive film.